The SIP protocol (RFC 3261) and Session Description Protocol (SDP) (RFC 4566) have been successful at delivering session control and presence applications from SIP Feature Servers to SIP User Agents (UAs). Common applications for SIP control include VoIP telephony, presence, messaging, video conferencing and whiteboarding. SIP is supported by a variety of UAs such as SIP hardware devices (e.g., desk phones) and SIP software clients running on personal computers or mobile devices (e.g., phones, tablets). Many SIP-based system implementations include Feature Servers providing advanced applications to support large network deployments.
However, typical SIP UAs that cannot use browser software (e.g., desktop phones) require dedicated, expensive SIP hardware and software in order to establish a communication session with other devices. As more and more web-based communication sessions migrate to website application servers using web protocols like WebRTC, older SIP UAs unable to communicate with a web-based system are in danger of being rendered obsolete—resulting in significant costs to replace these SIP devices.